1. Field of the Invention
The present invention is generally related to hard disk drives and, in particular, to the circuits, systems and algorithms for adaptively controlling the performance of the data read/write channel electronics to optimally match the electrical and electromagnetic characteristics of the heads and media of the disk drive.
2. Description of the Related Art
The design of conventional disk drives must necessarily take into account the inevitable tolerance variations in the drive's components. In particular, the data read/write error rate is premised on the combined tolerances of the precision components that make up the largely analog data processing circuits of the read/write data channel electronics. However, the effectiveness of the channel electronics in minimizing errors is, in substantial part, also dependent on the particular construction of the hard disk assembly (HDA), including the media's coercivity and thickness, the nominal flying height of the read/write head and the head's own electromagnetic characteristics, and the specific resistive, capacitive and inductive characteristics of the electrical connection between the head and the read/write channel electronics.
In a theoretical worst case analysis, the error rate is calculated on the sum total of the worst case tolerance variances of the individual components and subsystems in the read/write data channel and HDA. As a practical matter, data error rate calculated in this manner would be extremely low. Rather, in typical practice, assembled disk drives are first tested to determine whether they meet the probable performance of the drive as designed. Once published specifications are established for the drive manufacturing line, drives are tested to determine whether they continue to meet the published specifications. Where a drive is failed due to a high data error rate, the drive is analyzed to determine the components contributing the greatest amount to the error rate. The drive, when and to the extent reasonable, is then reworked to fix or replace the error prone components or, where the cost of such repairs would be to high, simply scrapped.
Naturally, the aggregate manufacturing cost of the drives are directly increased in proportion to the number of drives that must be reworked or scrapped. A typical strategy, Where higher than expected number of the drives are initially failed, is to modify if not reduce the specifications of the drive to pass sufficient numbers of the drives to make continued production commercially feasible.
A conventional alternative strategy is to implement an engineering design change to improve on the precision of the most typically failure causing components. Where the change is technically feasible, the cost of higher precision components, as well as the cost of implementing the design change, again directly impacts the aggregate cost of drive manufacture. When implemented, the design change is applied to all of the drives manufactured.